The invention relates to an electrode, and to the use of the electrode in electrometallurgical processes.
Electrometallurgical processes such as electrorefining, electrowinning, electroforming, etc., employ electrodes as is well known in the art. While the present invention discloses an electrode structure applicable in such processes, the description which follows will be primarily directed to the electrorefining of copper
In general, the electrorefining of copper comprises forming blister copper anodes by melting and casting, followed by electrodepositing copper over a 1-2 week period onto pure copper starting sheets in production cells from the impure anode. The pure copper cathode product is then melted and processed into the desired forms such as wire bar, rod, billet, etc. It will be understood by those skilled in the art that the blister copper anodes contain about 98% copper and minor amounts of impurities, whereas pure copper electrodeposited on a cathode either as a starting sheet or final product contains about 99.99% copper.
The starting sheets are thin sheets of pure copper usually having a thickness of about 0.5 to 0.7 millimeters (mm.) and are generally produced in special stripper cells by a 24-hour electrodeposition of copper onto a starter blank from an impure anode, usually called a stripper anode. The starter blank may be made of various metals, such as copper, stainless steel and titanium, and the procedures of deposition are generally the same as in production cells to make pure copper cathode except for the daily withdrawal and stripping of the thin copper starting sheet deposit from the starter blank. The final preparation of the starting sheets may comprise stripping from the blank, washing, straightening and stiffening, trimming to the desired size and attaching cut starter sheet loops for support in the production cell. Some processes deposit copper on the starting blank over a longer period to produce copper cathode product which is also stripped from the blank but then melted and processed into the desired final form. The deposits are generally greater than 2 mm.
Unfortunately, however, the preparation of starting sheet has been a continuing problem for the electrorefining industry because the required high standards of quality result in a high scrap rate in the process. Firstly, the starting sheet is generally of a fixed dimension limited by the size of the electrodepostion tank and it is industrially important that the anode be of optimum size because of the high cost in energy and labor of making the anode and reprocessing of anode scrap remaining after electrodeposition. The anode however, must still provide substantially complete and even coverage over the starting blank and the problem facing industry has been to correlate the anode size with the size of the starter blank to minimize the electrorefining cost.
Thus, if the copper is not deposited completely over the surface of the starter blank, the starter blank may be damaged and the starter sheet would be unacceptable for cathode production. Further, if parts of the starter blank contain too thick a deposit, the sheet will be more difficult to strip and may not be trimmable to its final size. The disposition of the above unacceptable sheets require increased energy and manpower usuage which add considerably to the electrorefining cost.
To overcome these problems and to reduce electrorefining costs, industry has over the years developed anodes which are slightly smaller in dimension than the starting blanks. For example, the anode dimensions are usually about 80-90%, e.g., 90-95%, of the starting blank dimensions. Thus, if a starting blank were 10 inches wide by 20 inches high, the anode would be about 9 inches wide by 18 inches high. These anodes, however, are not completely acceptable as discussed hereinabove and attempts to modify the anode design by increasing or decreasing the dimensions have met with limited, if any, success.